South Jersey Skies: Eggs on the equinox

View full sizeDr. Phil Plait, the "Bad Astronomer," balancing eggs when it wasn't an equinox.If you've been living in the United States at any time in the last two or three decades, you've heard of the story that one can balance an egg on its end on the day of the equinox, and on no other day. I'll bet you even heard it yesterday.Keith JohnsonAt first glance, this is a pretty remarkable claim. Carl Sagan once declared, “Extraordinary claims demand extraordinary evidence.” So every March 20 (or March 21— the date varies slightly from year to year), school classes take out dozens of eggs, go to their chemistry labs with their solid tables, to test the theory. They usually manage, after considerable effort, to get several of them to stand up on their tips, on both the narrow ends and the broad ends. You can find numerous pictures of these successes on the Web.

But the other side of the hypothesis must be tested as well. If today is not the equinox, the theory predicts that you should not be able to do it. Does that claim stand up? If the eggs don't stand up, the claim does!

The answer is, no, it doesn't. Well-known “Bad Astronomer” Phil Plait (blogs.discovermagazine.com/badastronomy) tried it in late October some years ago, more than a month after the fall equinox, and managed to get three eggs up on end. His wife surpassed him with five (you can find pictures of Plait's eight eggs on the Web.)

Eight eggs a-balancing — even when it's not an equinox.

I've done it myself. The largest number I've come across is 17 dozen (though that's unsubstantiated.) Be aware that this does require a certain amount of dexterity!

Proponents of the theory claim that eggs can stand up when the Sun is lined up with the top of the egg, so that its gravity helps the egg stay balanced. But there are at least two things wrong with this idea.

On the equinox, the Sun lies directly over the Earth's equator. So if you stand an egg up at local noon in Ecuador, the Sun's gravity will indeed be pulling at the top of the egg.

But not in South Jersey. The Sun will be only 50 degrees above the horizon, only five degrees more than halfway up the sky. That's nowhere near straight up! You'd have a better chance at the summer solstice in June, when the Sun is about 16 degrees from straight up, but even then the alignment would be far from good.

Moreover, if you're looking for a place on the Earth where the Sun is straight up, there's always such a place! Such a spot can always always be found in the Equatorial Zone. To locate the current one for this particular moment, just draw a line from the Earth's center to the Sun. It will come out somewhere in the tropics. The existence of “straight-up spots” has nothing to do with the equinoxes.

Where did the “Eggy Equinox” theory come from? Plait claims that the idea originated in a story that appeared in Life magazine in 1945. Reporter Annalee Jacoby found that the Chinese had a ritual of balancing eggs on end on the first day of spring, called Li Chun. The story stimulated interest in America, and people started making the attempt on equinox day each year.

But there's an important part of the story that got left out. The Chinese, like many other cultures, do not consider the equinox to be the beginning of spring! Instead, they pick a day roughly a month and a half earlier for Li Chun, the season's start. The equinox comes in the middle of spring by this plan. The Chinese balanced their eggs in early February!

You might ask, why does the egg stand on end at all? Plait proposes that miniscule bumps in the shell of the egg make it possible, if difficult, to find a spot on the egg where a set of bumps, acting like legs on a tripod, allows the egg to sit upright. In support of this, he mentions that especially smooth eggs are more difficult to balance than rougher ones. It seems like a reasonable notion. Someone should test it.

Unfortunately, our equinox day was yesterday, March 20, so you can't test the first half of the theory this month (but think about doing it next autumn, at the other equinox.)

The second half of the theory is still testable, however. I encourage everyone to give it a try today, or next week, or next month. Doing your own science can be eggciting!

Equinox event. The annual Equinox lecture will be given in the Betty Long Rowan auditorium in Rowan Hall (the engineering building) at 7 p.m. March 25. Dr. Mark Devlin of the University of Pennsylvania will present the lecture, entitled “Finding Half the Starlight in the Universe: Adventures with the BLAST Experiment.” This lecture is free and open to the public. More information about the experiment is available at www.blastexperiment.info.

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Keith Johnson, director of Rowan University's Edelman Planetarium, apologizes for the egg pun above (but it was a pretty good yoke, wasn't it?) and welcomes photos or descriptions from anyone who succeeds — or fails! — to balance an egg on a non-equinox day. You can send your reports, pictures, and questions to him at johnsonk@rowan.edu.

The planetarium is now offering the star show, “Skywatchers of Ancient Mexico,” and the laser show, “Pink Floyd: The Wall,” on Saturday nights. Information can be found at the planetarium Web site, www.rowan.edu/planetarium/.